I’m enjoying the conference, and have managed to fit in a number of very illuminating discussions with colleagues from other institutions, which is really the most useful part of conferences anyway, as everyone knows. Plus, I finally got to meet the only one of my co-bloggers that I’d never met before. Furthermore, the talks have generally been good – well thought through, and eloquently presented – and we had a lovely reception last evening at the beautiful Detroit public library, where I snapped the mural, which seemed appropriate (except for the pecs). Nevertheless, the overwhelming vibe that I’m getting here is one of extreme impatience and anticipation. This, of course, is all about the Large Hadron Collider (LHC).

There have been talks presenting rather recent and significant results, of course – for example Angela Olinto‘s talk about high energy cosmic rays and gamma rays was a lovely survey of the combined data from Fermi, Auger, PAMELA, ATIC, and other experiments; Josh Frieman‘s talk on cosmology, and particularly cosmic acceleration, provided a clear picture of the vibrancy of the field and the great progress that has been made over the last decade; and there are numerous other interesting talks coming up on QCD, heavy ion physics, neutrinos, etc.. But in high-energy particle physics I think we’re mostly seeing talks, albeit good talks, summarizing things we’ve seen again and again for a long time. The details of the LHC detectors (ATLAS, CMS, LHCb and ALICE); how one hopes to tease out evidence for the Higgs from the data; ditto for supersymmetric particles, and those arising from large extra dimensions; and a talk by Lyn Evans summarizing the progress towards getting the LHC back online after last year’s calamity.

Particle physics is screaming out for a new result pointing the way to the physics that we know must lie beyond the unreasonably successful standard model. We know this physics should be there because of purely particle physics problems, such as the hierarchy problem – why is the weak scale so much lower than the Planck scale, and stable against quantum corrections – but also because cosmological observations such as the matter antimatter asymmetry of the universe and dark matter tell us that new particles and interactions must be out there, perhaps at the energy scale of the LHC.

People aren’t sitting around twiddling their thumbs and just waiting for the machine to turn back on, of course. And none of what I’ve written above is in any way intended as a criticism. Ongoing work at existing experiments (such as those at the Tevatron, for example) is placing new limits (for example the recent claimed exclusion of a Higgs mass between 160 and 170 GeV), and experimentalists are busy refining their techniques for extracting the maximum amount of information from the upcoming LHC data. This is all extremely important work, and certainly very interesting. But it doesn’t change the fact that people really want the LHC.

And it isn’t just pure particle physicists who feel this way. Those of us in particle cosmology have been getting a wealth of data from cosmology for a while now. But this has left us in a position where dark matter and cosmic acceleration are on such a firm footing that more than ever we desperately need to understand how these phenomena fit into our understanding of fundamental physics. The LHC is the next essential tool in this quest. New physics discovered there may have direct implications for cosmology. And if it doesn’t, then proposed theoretical explanations will be constrained by, and may well open up new vistas for, cosmology.

So we’re all, particle physicists and cosmologists, keeping our fingers tightly crossed for the planned turn on later this year.

Particle cosmology is the application of lessons learned in high-energy physics to the study of cosmology. A closely-related and often overlapping field is astroparticle physics, which is the application of high-energy physics to astrophysics.

The basic idea is that our knowledge of the universe is now sufficiently detailed our knowledge of high-energy physics can be directly applied into our computations of the behavior of various astrophysical and cosmological phenomena, to the point where we can even make statements about the properties of high-energy physics by looking at astrophysical and cosmological phenomena.

Examples include the study of ultra high-energy cosmic rays, pulsars, supernovae, and other energetic phenomena, as well as very early times in our universe.

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Cosmic Variance

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About Mark Trodden

Mark Trodden holds the Fay R. and Eugene L. Langberg Endowed Chair in Physics and is co-director of the Center for Particle Cosmology at the University of Pennsylvania. He is a theoretical physicist working on particle physics and gravity— in particular on the roles they play in the evolution and structure of the universe. When asked for a short phrase to describe his research area, he says he is a particle cosmologist.